There are many reasons that manufactured parts receive a unique identifier such as a serial number. Two of the most common reasons are to enable traceability of a part throughout its lifecycle and to insure the part is not a counterfeit. Traceability is normally accomplished by marking the part with a unique identifying code, or fingerprint. This can be accomplished by printing, for instance a label on a computer or the serial number on currency, or by stamping the code into a metal or plastic piece, for instance a vehicle identification number (VIN) or a firearm serial number. Unfortunately, such methods are subject to counterfeiting techniques. Labels are easily removed, and can be copied even if they contain advanced features such as holograms or embedded fibers. Stamped codes can also be removed or replicated. Techniques have been developed to try and recover a serial number after a criminal has filed the number off of a firearm, but this is an expensive process and not always successful.
Attempts have been made to include a unique identifier within the interior of a part so as to make removal, alteration, or replication of the identifier more difficult. For instance, with the advent of additive manufacturing, attempts have been made to include the serial number or other identifying mark within the bulk of a manufactured part.
Additive manufacturing refers to any method for forming a three-dimensional object in which materials are deposited according to a controlled deposition and/or solidification process. The main differences between additive manufacturing processes are the types of materials to be deposited and the way the materials are deposited and solidified. Some methods extrude materials including liquids (e.g., melts or gels) and extrudable solids (e.g., clays or ceramics) to produce a layer, followed by spontaneous or controlled curing of the extrudate in the desired pattern. Other processes deposit solids in the form of powders or thin films, followed by the application of energy and/or binders often in a focused pattern to join the deposited solids and form a single, solid structure having the desired shape. In some methods, successive layers are individually treated to solidify the deposited material prior to deposition of the succeeding layer, with each successive layer becoming adhered to the previous layer during the solidification process. Welding and casting can also be considered additive manufacturing methods. For instance areas of a casting mold can be locally cooled or heated, which can result in controlled and localized areas of the product having different porosity, density, etc.
Methods for uniquely marking objects formed according to an additive manufacturing process have been disclosed. Such methods include, for example, the addition of an identification tag within a layer or between layers; the formation of a pattern within one or more layers, such as the deposition of the material in a pattern of ones and zeros or other symbols in a recognizable fashion; or the deposition of a secondary material within a layer, optionally according to a predetermined distribution pattern. While such methods can produce an identifiable mark within a structure that can often be examined according to known non-destructive examination techniques, the identifiable marks are still subject to counterfeiting, which is becoming easier with the decrease in cost of additive manufacturing devices and processes.
What are needed in the art are methods for formation of a unique identifiable mark that is not subject to counterfeiting within or on a structure formed according to an additive manufacturing process. The manufactured parts thus formed can be uniquely recognized and identified for secure tracing and counterfeiting prevention.